In a refrigerating and air-conditioning apparatus that uses a non-azeotropic refrigerant mixture, since the boiling points of refrigerants included in the non-azeotropic refrigerant mixture are different from each other, the composition of the circulating refrigerant may change. Particularly, when the size of a refrigerating and air-conditioning apparatus is large, a change in the refrigerant composition becomes noticeable. As described above, when the refrigerant composition changes, changes in the condensing temperature or the evaporating temperature may occur even there is no change in the pressure. In other words, an improper refrigerant saturation temperature at a heat exchanger hinders the refrigerant from being readily condensed and liquefied or evaporated and gasified at the heat exchanger, and the heat exchange efficiency may be reduced.
In addition, when the refrigerant composition changes, changes in superheat or subcooling may occur even there are no changes in the temperature and pressure at the refrigerant discharge side of the heat exchanger. In other words, owing to improper superheat before the refrigerant is sucked onto a compressor, a liquid refrigerant flows into the compressor, whereby the compressor may consequently be damaged; or owing to improper subcooling before the refrigerant flows into an expansion valve, the refrigerant comes into a gas-liquid two-phase state, whereby generation of refrigerant sound or an unstable phenomenon may consequently occur.
Here, it is known that a refrigerating and air-conditioning apparatus including a refrigerant storage container (receiver) at a high-pressure side has a smaller fluctuation range of the composition of a circulating refrigerant than that of a refrigerating and air-conditioning apparatus including a refrigerant storage container (accumulator) at a low-pressure side. However, when refrigerant leak occurs at a refrigeration cycle, the fluctuation range of the refrigerant composition is increased regardless of whether the refrigerant storage container is at the low-pressure side or the high-pressure side. In other words, it is possible to detect refrigerant leak by detecting a fluctuation of the refrigerant composition.
Thus, various refrigerating and air-conditioning apparatuses including means for detecting a refrigerant composition in order to suppress reduction in heat exchange efficiency, to avoid compressor damage, to suppress generation of refrigerant sound, to suppress an unstable phenomenon, and to detect refrigerant leak, have been proposed.
As such a refrigerating and air-conditioning apparatus, a refrigerating and air-conditioning apparatus has been proposed which includes a bypass connected so as to bypass a compressor and in which a double pipe heat exchanger and a capillary tube are connected to the bypass (e.g., see Patent Literature 1). In the technology described in Patent Literature 1, the temperature at the refrigerant inflow side of the capillary tube, the temperature at the refrigerant outflow side of the capillary tube, and the pressure at the refrigerant outflow side of the capillary tube are detected, and a refrigerant composition is calculated on the basis of these detection results.
In addition, as such a refrigerating and air-conditioning apparatus, a refrigerating and air-conditioning apparatus has been proposed which detects an excess refrigerant amount within an accumulator and calculates a refrigerant composition (e.g., see Patent Literature 2). In other words, in the technology described in Patent Literature 2, a refrigerant composition is calculated on the basis of a correlation between information such as the number of operating indoor units and the outside air temperature and a previously obtained refrigerant composition, an excess refrigerant amount within the accumulator is detected, and the calculated refrigerant composition is corrected, whereby the composition of a circulating refrigerant is calculated.